(a) Field of the Invention
The present invention relates to a method and apparatus for multicast transmission in a wireless network.
(b) Description of the Related Art
A wireless local area network (WLAN) has been widely used in a home and a business. A wireless LAN technology represented by IEEE 802.11 can wirelessly connect the networks through an air interface.
Meanwhile, when wirelessly connecting the networks, it can be easily exposed to an interference such as multipath, collision, noise, etc. Thus, it is difficult to transmit data reliably. In particular, the wireless LAN is more difficult to transmit data with reliability in multicast transmission simultaneously transmitting data to a plurality of receivers in characteristics of a medium access control (MAC) layer.
In the wireless LAN environment, a forward error correction (FEC) scheme is considered for a reliable multicast transmission. According to the FEC scheme, a transmitter carries additional bits with each packet. When an error occurs, a receiver uses the additional bits to recover the error. According to the FEC scheme, when communicating in the wireless environment with large error probability or transmitting large packet, a large amount of bandwidth is wasted. In addition, when collisions between frames transmitted from a plurality of transmitters occur, a receiver cannot recover error.
In addition, in the wireless LAN environment, a packet retransmission scheme using acknowledgement/negative-acknowledgement (ACK/NACK) is considered for the reliable multicast transmission. According to the packet retransmission scheme, each receiving station reports the receiving state of the data packet to a transmitting station and the transmission station recovers error by retransmitting a lost data packet. However, the packet retransmission scheme has a problem in that the packet retransmission probability is linearly increased based on the number of receiving stations. For example, in a unicast transmission that a single transmitting station transmits packets to a single receiving station, when the packet error probability is 0.001, the transmission station retransmits one packet every time it transmits 1000 packets. However, in the multicast transmission that a single transmitting station transmits packets to 100 receiving stations, when the packet error probability is 0.001, the transmitting station retransmits one packet every time it transmits 10 packets. As described above, in the multicast transmission, a number of retransmission of packets is increased in proportion to the number of receiving stations. Thus, performance of the system is deteriorated.